HR: 09:15h
AN: T51F-06    [Abstracts]
TI: The Sub-Seafloor Structure of Mid-Atlantic Ridge Core Complexes
AU: * Canales, J
EM: jpcanales@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543, United States
AU: Xu, M
EM: minxu@mit.edu
AF: Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Tucholke, B E
EM: btucholke@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543, United States
AU: Collins, J A
EM: jcollins@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543, United States
AU: Dubois, D L
EM: ddubois@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543, United States
AB: Oceanic core complexes form by long-lived extension along detachment faults (in some instances for periods more than a million years), exposing sub-volcanic lithosphere at the seafloor. Seafloor sampling and deep drilling indicate that highly altered mantle peridotites and lower crustal gabbros are the dominant lithologies in these structures, but their relative abundance and distribution beneath the detachment surfaces are not well constrained, which hinders our understanding of the origin, composition, and evolution of core complexes. Here we present results from a geophysical study aimed at determining the sub-seafloor P-wave seismic velocity structure of three of the best developed and most studied oceanic core complexes (CC) found on the Mid-Atlantic Ridge: Kane CC located on ~3.3-2.1 Ma lithosphere of the North American plate immediately to the south of Kane FZ (23° 20'-37'N), Dante's Domes CC located on ~2.1-0.7 Ma African-plate lithosphere at 26° 35'-45'N, and Atlantis CC located on ~2.0-0.8 Ma lithosphere of the North American plate immediately to the north of Atlantis FZ (30°05'-20'N). We use seismic data acquired in 2001 along and across the three core complexes using the 6-km-long hydrophone streamer and air-gun array of the R/V Ewing (cruise EW0102). The dense sampling of sources and receivers and the relatively shallow seafloor of the study areas allow us to perform traveltime tomography inversions to image lateral variations in seismic velocity at lateral scales of 1 km or less within the upper ~0.5-1.5 km of the lithosphere. Our results show that the seismic velocity structure within each CC is highly heterogeneous, but that remarkably similar patterns in velocity structure exist among the three CCs. In a broad sense, the velocity structure of each of the three CCs is characterized by three distinct patterns: (1) areas with relatively high velocities (>4 km s^-1) and high velocity gradients (>3 s^-1) near the seafloor, (2) areas with moderate seafloor velocities (3.5-4 km s^-1) and less-pronounced velocity gradients (~1.25- 2.5 s^-1), and (3) areas with low seafloor velocities (<3.5 km s^-1) and low velocity gradients (<1.25 s^-1). We interpret the lithological correlation of the velocity structures by integrating our results with the extensive seafloor geological sampling available from the Kane CC and the geological sampling and deep drilling results at the Atlantis CC (IODP Hole U1309D). The lowest seismic velocities/gradients generally correspond to volcanic terrain and an abundance of in situ pillow basalts; areas with moderate velocities/gradients correspond to predominance of highly altered mantle peridotites; and the highest velocities/gradients indicate a predominance of gabbros. If our interpretations are correct, then the observed seismic velocity patterns indicate that the corrugated CCs have exhumed both gabbro and mantle-derived serpentinite sections. These sections can be as large as 5-20 km wide in plan view, and they exhibit complex lateral variations in both strike and dip directions.
DE: 3025 Marine seismics (0935, 7294)
DE: 3035 Midocean ridge processes
DE: 3036 Ocean drilling
DE: 3075 Submarine tectonics and volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting